1. Field of the Invention
The present invention relates to a radiation measuring device forming a radiation monitor used for emission management or radiation management in a nuclear reactor installation and a spent fuel reprocessing facility and to a diagnostic method thereof.
2. Background Art
A requirement for a radiation measuring device used in a nuclear reactor installation, a spent fuel reprocessing facility, and so forth is an ability to enable measurement covering a broad range of the input repetition frequency of a signal pulse as the detection result of radiation in the order of 10 cpm to 107 cpm. In order to eliminate discontinuity accompanying range switching, count rate measurement using an up/down counter operating at a high speed in a broad range without switching ranges is carried out. According to this measuring method, a count rate is computed by reading an integrated value when an addition input of the up/down counter and a subtraction input following with a first order lag of a time constant are balanced by a computing unit in a fixed cycle, and this method is characterized particularly in that a high count rate can be measured. An example is described in JP-A-2008-215907.
When an online diagnostic is made on the count rate measurement using an up/down counter from the outside, for example, a pulse height analyzer and a controller are used. Upon input of a signal pulse from a detector, the pulse height analyzer measures a spectrum for a predetermined measurement time. Meanwhile, the spectrum data from the pulse height analyzer and the count rate of the computing unit are inputted into the controller. The controller finds an integrated count within a predetermined pulse height range on the basis of the spectrum data and then divides the integrated count by the measurement time to find a count rate. A diagnosis is made by comparing the count rate thus found with the count rate of the computing unit. Examples are described in JP-A-2001-215279 and JP-A-6-324158.
However, because of the configuration as described above, the radiation measuring device in the related art has a problem that the scale of the device becomes large. In addition, in order to make a high-accurate diagnosis, the controller has to control the up/down counter and the pulse height analyzer to be in synchronization with each other so that pulse trains in the same time zone of the same time axis are captured as an input to the up/down counter and an input to the pulse height analyzer. However, because the time constant of the up/down counter varies in real time, it is, in principle, difficult to bring the captured pulse train of the up/down counter into coincidence with the captured pulse train of the pulse height analyzer. This difficulty raises another problem that a diagnostic accuracy cannot be improved.